Fowler's zoo and wild animal medicine: current therapy

349 Pages·2003·2.199 MB·English

by  R Eric Miller, Murray E Fowler

CONTENTS
Contributors to Volume 47 . . . . . . . . . . . . . . . . . . . . vii
Milk Protein Modification to Improve Functional
and Biological Properties
Jean-Marc Chobert
I. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 1
II. ChemicalModification of MilkProteins . . . . . . . . . . . 2
III. Enzymatic Protein Processing . . . . . . . . . . . . . . . . 37
IV Genetic Engineering of MilkProteins andProteases . . . . . 50
V. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . 58
Acknowledgements . . . . . . . . . . . . . . . . . . . . . 60
References . . . . . . . . . . . . . . . . . . . . . . . . . 60
The Nutritional Significance, Metabolism and Toxicology
of Selenomethionine
Gerhard Norbert Schrauzer
I. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 74
II. Properties ofSelenomethionine . . . . . . . . . . . . . . . 74
III. Methods ofAnalysis . . . . . . . . . . . . . . . . . . . . 75
IV. Synthesis . . . . . . . . . . . . . . . . . . . . . . . . . 77
V. Natural Occurrence and Biosynthesis . . . . . . . . . . . . 77
VI. Selenomethionine-containingProteinsand Enzymes . . . . . 82
VII. MetabolismofSelenomethionine . . . . . . . . . . . . . . 86
VIII. Selenomethionine inHuman Se Supplementation . . . . . . 91
IX. SeYeast asan Animal Feed Supplement . . . . . . . . . . 92
X. Toxicity ofSelenomethionine . . . . . . . . . . . . . . . . 94
XI. Selenium Requirements andRecommendedDietary Intakes . 101
XII. Summary and Conclusions . . . . . . . . . . . . . . . . . 102
References . . . . . . . . . . . . . . . . . . . . . . . . . 102
vi CONTENTS
Echinacea as a Functional Food Ingredient
Clifford Hall III
I. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 113
II. PhytochemicalConstituents . . . . . . . . . . . . . . . . . 117
III. Standardization,Quality Assurance andRegulations . . . . . 144
IV. Biological and Toxicological Activities . . . . . . . . . . . 148
V. Echinacea as aFunctional Food Additive . . . . . . . . . . 161
VI. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . 164
Acknowledgements . . . . . . . . . . . . . . . . . . . . . 165
References . . . . . . . . . . . . . . . . . . . . . . . . . 165
Bioactive Peptides and Proteins
Anne Pihlanto and Hannu Korhonen
I. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 175
II. BioactiveFoodProteins and their Biological Functions . . . 176
III. BioactivePeptides Derivedfrom Food Proteins . . . . . . . 207
IV. Technological Processes for the Production ofBioactive
Proteinsand Peptides . . . . . . . . . . . . . . . . . . . . 237
V. Safety Implications . . . . . . . . . . . . . . . . . . . . . 247
VI. ResearchNeeds . . . . . . . . . . . . . . . . . . . . . . 248
References . . . . . . . . . . . . . . . . . . . . . . . . . 249
Plant Products with Hypocholesterolemic Potentials
Pulok K. Mukherjee
I. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 278
II. Phytoconstituentswith Hypocholesterolemic Potentials . . . . 281
III. Herbs Useful inHypercholesterolemia . . . . . . . . . . . . 298
IV. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . 322
Acknowledgements . . . . . . . . . . . . . . . . . . . . . 324
References . . . . . . . . . . . . . . . . . . . . . . . . . 324
INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339
CONTRIBUTORS TO VOLUME 47
Numbersinparenthesesindicatethepageonwhichtheauthors’contributionsbegin.
Jean-Marc Chobert, Laboratoire d’Etude des Interactions des Mole´cules
Alimentaires, Institut National de la Recherche Agronomique, Rue de la
Ge´raudie`re, B.P. 71627, 44316 Nantes Cedex 3, France (1)
Clifford Hall III, 324 IACC, Department of Cereal and Food Sciences,
North Dakota State University, Fargo, ND 58105, USA (113)
Hannu Korhonen, MTT Agrifood Research Finland, Food Research,
31600 Jokioinen, Finland (175)
Pulok K. Mukherjee, Department of Pharmaceutical Technology,
Natural Product Studies Laboratory, Jadavpur University, Kolkata
700032, India (277)
Anne Pihlanto, MTT Agrifood Research Finland, Food Research, 31600
Jokioinen, Finland (175)
GerhardNorbertSchrauzer,BiologicalTraceElementResearchInstitute,
2400 Boswell Rd., Suite 2000 Chula Vista, CA 91914, USA (73)
MILK PROTEIN MODIFICATION TO IMPROVE
FUNCTIONAL AND BIOLOGICAL PROPERTIES
JEAN-MARC CHOBERT
Laboratoired’EtudedesInteractionsdesMole´culesAlimentaires
InstitutNationaldelaRechercheAgronomique
RuedelaGe´raudie`re
B.P.71627,44316NantesCedex3
France
I. Introduction
II. ChemicalModificationofMilkProteins
A. Phosphorylation
B. Esterification
C. Glycationofb-lactoglobulinUsingMildConditions
D. Thermal Modifications of Structure and Co-denaturation of
a-lactalbuminandb-lactoglobulin
III. EnzymaticProteinProcessing
A. LimitedProteolysisandFunctionalProperties
B. Allergenicity
C. BitterPeptides
D. TransglutaminaseandDairyProducts
E. LiberationofBiologicallyFunctionalPeptides
IV GeneticEngineeringofMilkProteinsandProteases
A. Thermostabilityofb-lactoglobulin
B. Gelationofb-lactoglobulin
C. DesignofRecombinantEnzymesUsedforProteinModification
V. Conclusion
Acknowledgements
References
I. INTRODUCTION
The actual and potential use of milk proteins as food ingredients has been a
popular topic for research over the past 30 years. Milk and dairy products
have numerous advantages over competitors when used as ingredients: they
are colorless, have a bland taste, are rather stable to processing, are free of
ADVANCESINFOODANDNUTRITIONRESEARCHVOL47 q2003ElsevierInc.
ISSN:1043-4526 Allrightsreserved
DOI:10.1016/S1043-4526(03)47001-0
2 J.-M.CHOBERT
toxins and have constituents that can be easily fractionated. As ingredients,
dairy products are used mainly for their physico-chemical properties.
The effective utilization of proteins in food systems is dependent on
tailoringtheprotein’sfunctionalcharacteristicstomeetthecomplexneedsof
themanufacturedfoodproducts.Manyfoodproteinsrequiremodificationto
improve such functional properties as solubility, foaming and emulsifying
activity (EA). Reviews on classical food proteinmodifications for improved
functionalityareavailableintheliterature(MeansandFeeney,1971;Feeney
and Whitaker, 1977, 1982, 1986).
Functionalpropertiesofproteinsarecloselyrelatedtotheirsize,structural
conformation, and level and distribution of ionic charges. Chemical
treatments,whichcouldcausealterationoftheseproperties,includereactions
that either introduce a new functional group to the protein or remove a
componentpart from the protein.Consequently, reactionssuch as acylation,
phosphorylation, esterification, glycation, limited hydrolysis, and deamida-
tion have been used to impart improved functional properties to the dairy
proteins.
Thisreviewconcernssomechemical,enzymaticandgeneticmethodsthat
modify dairy proteins with an emphasis on current developments.
II. CHEMICAL MODIFICATION OFMILK PROTEINS
Primarystructureofproteinscanbechemicallymodifiedinordertoimprove
theirfunctionalproperties.Thisapproachhasbeenusedwithsuccesstostudy
thestructure–functionrelationships(enzymaticfunction,biologicalfunction,
physico-chemical and functional properties). Deliberate chemical modifi-
cationoffoodproteinscanresultinalterationofthenutritivevalue,formation
of potentially toxic amino acid derivatives, and contamination by toxic
chemicals.
Alteration of amino acid residues can be obtained by heating at acid or
alkaline pH. Main classes of reactions used to chemically modify the side-
chain of amino acids are acylation, alkylation, oxidation and reduction
(Figure 1). Some of them are described in this chapter.
A. PHOSPHORYLATION
1. Reaction conditions
Phosphorylationisaneffectivewaytoincreasenegativechargesinaprotein
moleculeandtherebytoimprovefunctionality,particularlysolubility.Either
O- or N-esterification reactions can transfer inorganic phosphate (P)
i
MILKPROTEINTAILORING 3
to proteins. In an O-esterification reaction, P reacts with the primary or
i
secondary hydroxyl on seryl or threonyl residues, respectively; or with the
weakly acidic hydroxyl on tyrosyl residue, forming a –C–O–Pi bond. In
N-esterification, P combines with the 1-amino group of lysyl residue, the
i
FIG.1. Mainchemicalmodificationsoffoodproteins.
4 J.-M.CHOBERT
FIG1. (continued)
imidazolegroupofhistidylresidue,ortheguanidinogrouporarginylresidue,
forming a –C–N–P bond. The nitrogen-bound phosphates are acid labile
i
and are readily hydrolyzed at pH values at or below 7. Proteins containing
oxygen-bound phosphate are acid stable and are the modification of choice
for food proteins since the pH of most food systems is 3–7 (Shih, 1992).
Enzymaticphosphorylationbyphosphorylasesandphosphatasesproduces
phosphoesters such as phosphoserine and phosphothreonine. Chemical
phosphorylation of proteins changes their functional properties, improving
themsometimes(Yoshikawaetal.,1981;Hirotsukaetal.,1984;Huangand
Kinsella,1986;Chobertetal.,1989;Matheis,1991).However,theproperties
ofthephosphorylatedproteinsdependentirelyonthedegreeofdenaturation
and substitution defined by the reaction conditions and the protein (Medina
etal.,1992;Sitohyetal.,1994).Caseinwasphosphorylatedbythecommonly
used methods, characterized by use of excessive amounts of phosphorus
oxychloride and with important additions of concentrated inorganic bases
(Matheis et al., 1983; Medina et al., 1992). Thus, obtained phosphorylated
caseins were highly cross-linked and partially insoluble and difficult
to characterize. Hence, there arose a need to produce monomeric over-
phosphorylated caseins more suitable for use and for study of their
MILKPROTEINTAILORING 5
functionalproperties.Themonomericformsaremorehydrophilic,andeasier
to study and used as additives. It was found that the outcome of
phosphorylation can be directed by the reaction conditions either towards
the formation of polymeric or predominately monomeric phosphoproteins
(Sitohy et al., 1994).
Whole casein, which originally contained 6molP/molprotein, bound an
additional 4, 7 and 11molP/molprotein when prepared with 25, 50 and
100molPOCl /molprotein in the presence of triethylamine (Sitohy et al.,
3
1995a). a-, b- and k-casein fractions containing 7, 4 and 1molP/molpro-
s
tein, respectively, bound an additional 21, 20 and 9molP/molprotein when
reacted with 100molPOCl /molprotein. The relatively lower extent of
3
phosphorylation achieved for the whole casein, as compared to a- or
s
b-casein fractions, might be due to the complexing effect between casein
componentsmakingsomefragmentsoftheproteinmoleculeinaccessiblefor
the reacting reagents. Alternatively, the relatively poor extent of k-casein
phosphorylation might be due to its hydrophobic nature (Kato and Nakai,
1980). Caseins with such properties were obtained not only by use of low
molar ratios of POCl (25–100molPOCl /molprotein) but also due to the
3 3
presence of triethylamine allowing the reaction to proceed with such low
POCl molarratios.Thephosphorylationyieldsobtainedintheseconditions
3
(low POCl /protein molar ratios; 25–100 in the presence of triethylamine)
3
were higherthan those obtainedbyMatheiset al.(1983)and evenhigher in
somecasesthanthoseobtainedbyMedinaetal.(1992)whousedextremely
highPOCl /proteinmolarratios(1000–2000)inthepresenceofaninorganic
3
base.
The SDS-PAGE patterns of the same samples showed small intermole-
cular associations in the phosphorylated caseins especially when compared
with the results obtained by Matheis et al. (1983) and Medina et al. (1992)
whosephosphorylatedsampleswereentirelyunabletoentertheSDS-PAGE
gel due to high cross-linking.
Thepossibilityofusingbasicaminoacidsintheformoffreebasesasthe
onlybaseofthereactionwasstudiedinordertoeliminatetheuseoftertiary
amines,whicharenutritionallyunacceptable(Sitohyetal.,1995b,c;Haertle´
and Chobert, 1999).
The extent of phosphorylation was proportional to the applied POCl /
3
protein molar ratios. Phosphoamidation was proportional to the basic amino
acid/POCl molar ratio, which is in agreement with the previously observed
3
importance of triethylamine acting as the proton scavenger (Sitohy et al.,
1994). The highest phosphorylation yield was observed for 80molPOCl /
3
molprotein and 6mol lysine or arginine acid/molPOCl . However, the
3
highestphosphorylationachievedvariedaccordingtothe(basic)aminoacid
used.Thisdifferenceisclearlyduetothedifferentnucleophilicityofthethree
6 J.-M.CHOBERT
amino acids used. The pK of the lateral groups of arginine, lysine and
histidineare12.48,10.53and6.0,respectively.Hence,thepHofthestarting
reaction media using L-arginine, L-lysine and L-histidine in the form offree
bases were 10.8, 9.7 and 7.6, respectively. It is well known that protonated
primary amines are unreactive. Thus, basic pH is essential for the rapid
formation of the phosphoamide bond. The obtained phosphorylation yields
might seem low but they may be acceptable for food purposes and they
are close to the highest phosphorylation (6molP/molcasein) reported by
Matheis et al. (1983) using 2000molPOCl /molprotein. The secondary
3
phosphoamide bond formation depends on the initial substitution of protein
with –POCl andyPOClshowinghigheryieldsforargininethanlysineand
2
confirmingtheroleofactivatedphosphategroupsinsecondarygraftingofthe
aminoacidsonb-lactoglobulin.Theuseofarginineorlysinemaybeadvised
as a reaction base for low phosphorylation yield. The secondary grafting of
the basic amino acid used for the reaction improved this method of
eliminatingtheunacceptablequaternaryamines(triethylamine).Whenother
aminoacidssuchasleucine,methionine,threonineortryptophanwereadded
(at a molar ratio of 2mol/molPOCl ) in addition to the basic amino
3
acid (molar ratio of 5mol/molPOCl ) to the reaction medium
3
(80molPOCl /molprotein), the phosphorylation yield was reduced to
3
2molP/molprotein. The arginine and lysine grafting yields were reduced
to 2mol amino acid/molprotein and the added amino acids did not form
significant amounts of secondary phosphoamide bonds. This indicates the
importance of the appropriate buffering by arginine and lysine conferred by
the basicity of their lateral side-chains.
2. Effect of phosphorylation of casein on its functional properties
The pH–solubility curves presented in Figure 2 generally show that
phosphorylated whole casein has greater solubility than native casein in
neutralandbasicpHsresultingfromthedisplacementoftheisoelectricpoint
towards acidic values. The gradual displacement of the isoelectric points
towards the acidic side demonstrates the gradual increase in the negative
charges with increasing phosphorylation yield. However, highly phosphory-
lated proteins are not resolubilized below their isoelectric point indicating
some cross-linking. The solubility curves of the phosphorylated casein
fractions (a , b and k) show the same dependence of solubility profiles
s
pointingtothemonomericstateofthemodifiedproteinssincethepolymeric
formispoorlysoluble andshows diffusechangesinthe isoelectric pointsas
previously found by Medina et al. (1992).
The emulsifying activity index (EAI) curves for phosphorylated whole
casein solution versus pH showed shift of their minima towards the acid